The present invention relates to a temperature control system for a permanent magnet system and in particular it relates to systems used for magnetic resonances imaging (MRI).
In such systems a magnetic field with a high degree of stability and homogeneity is essential for the successful application of a number of analytical techniques such as MRI. MRI systems comprising large amounts of permanent magnetic material can be used for the generation of such a magnetic field.
Most permanent magnetic materials with sufficient energy density to be useful for this application are generally very sensitive to temperature variations. The effect of the temperature variations on the air temperature of the permanent magnetic assembly can be reduced to tolerable levels by controlling the temperature of the permanent magnetic assembly. Thus, the temperature control of existing permanent magnet MRI assemblies rely on raising the temperature of the permanent magnetic assemblies so that heat flows to the ambient air. This technique, however, raises the temperature of the permanent magnetic assemblies and results in a significant reduction of field due to the large temperature coefficient of the permanent magnetic materials.
One object of the present invention is to provide a system for controlling accurately the temperature of the permanent magnetic assemblies.
According to the present invention there is provided a temperature control system for a permanent magnet system having at least one permanent magnetic assembly, in which the permanent magnet assembly is mounted in thermal contact with a yoke via a plurality of thermoelectric heat pumping devices. At least one temperature sensor is connected to an electronic control circuit; and the thermoelectric heat pumping devices are connected to and controlled by the electronic control circuit which controls the current passing through the thermoelectric heat pumping devices in dependence upon the temperature. In this way, the permanent magnet assembly is maintained at a desired temperature enabling the permanent magnet system to generate an accurate magnetic field.
According to an aspect of the present invention a thermoelectric heat pumping device is provided with a spring loaded plunger to provide mechanical pressure on the thermoelectric heat pumping device so that a good thermal contact between the thermoelectric heat pumping device and the permanent magnet assembly is achieved.
According to a further aspect of the present invention the thermal contact between the plunger and the yoke is achieved by a sliding fit of one end of the plunger with a hole in the yoke into which the said one end of the plunger is fitted.
According to still yet a further aspect of the present invention thermal grease is enclosed within said hole, and the plunger is provided with a ventilation hole to prevent displacement of the grease by trapped air as said one end of the plunger is inserted into said hole.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.